The present invention relates to an ultrasonic imaging apparatus, an image processing apparatus, and a program for producing time-varying tomographic image data, especially, tomographic image data representing an image of a contrast medium injected into a subject.
In recent years, an ultrasonic imaging apparatus has been used to image a subject by injecting a contrast medium into the subject. The contrast medium is a liquid containing numerous microscopic bubbles. The liquid injected into a subject circulates through the subject's body with the passage of time. Ultrasonic waves emitted from the ultrasonic imaging apparatus become nonlinear due to the microscopic bubbles in a region through which the contrast medium has circulated, and are observed as echoes having a harmonic.
When a contrast medium is injected into a subject in order to produce image data using an ultrasonic imaging apparatus, part of the image data carried by a harmonic represents a field into which the contrast medium is infiltrated. A time-sequential change of fields indicates the progress of infiltration or circulation of the contrast medium into or through a subject. The progress serves as information important to specify various diseases.
Moreover, even when image data is acquired using a color flow mapping (CFM) technique that does not employ a contrast medium, an image of a field displayed in colors according to the image data shows time-sequential or spatial circulation of blood, and provides information that is important to specify various diseases.
[Non-Patent Document 1] “Guide to Ultrasonic Contrast Imaging” (Fuminori Moriyasu et al., Kanehara Publishing, Feb. 28, 2003, p. 54-55)
However, according to the background art, the positional relationship between a region in a subject, in which a contrast medium lies and which is being imaged, and any other region into which the contrast medium may be infiltrated is not clarified. Namely, an image displayed on an ultrasonic imaging apparatus renders only a field in which the contrast medium lies and which is being imaged. The other fields cannot be discerned because of a low signal strength.
In particular, all fields in a subject into which a contrast medium is infiltrated during a period from the instant an image is initially displayed to the instant the image disappears cannot be discerned simultaneously. Nevertheless, when an operator interprets an image, pieces of image information representing the images of all the fields into which the contrast medium is infiltrated are very important to specify a field into which the contrast medium is infiltrated and which is being visualized and to recognize a time-sequential change of such fields.
Moreover, even when image data is acquired from blood flow using the CFM technique, an image of a field displayed in colors according to the image data partly shows time-sequential or spatial circulation of blood. It is important for an operator to discern all fields through which blood circulates time-sequentially or spatially.
Consequently, what counts is how to realize an ultrasonic imaging apparatus, an image processing apparatus, and a program that help an operator recognize all fields in a subject, into which a contrast medium is infiltrated, concurrently with a visualized region of the subject in which the contrast medium lies.